HI Guys,
On the Argosy 1 , PTO instability was caused by several factors.
When pushing on the top cover close to the front of the
set the frequency would move or jump several 100 cycles.
The solution to this is several fold;
a./ Remove the cover from the PTO box .There are only 2 screws
to provide shielding which is inadequate. You will find 1 or 2
sheets of an insulating type card inside the cover.This card
tends to isolate the contact between the PTO box and cover even
further making the problem worse. Wrap a layer of aluminum foil
around the insulating card and re-install it all together again.
You will have to re tune the slug coil to bring the pto back on
frequency.
b./Install fine spring wire wipers to wipe on the pto shaft
where it protrudes at the front .These wiper wires are secured
under the screws that hold the pto to the front chassis.
These wiper wires ground the shaft and counteract HAND
CAPACITANCE.Hand capacitance is a major culprit in the vfo
going off freq.The design of the PTO has the shaft isolated which
is unnecessary.
c./ Remove and discard the plastic sections that run front to
back and are located on both sides of the main enclosure.
Either replace these plastic units with metal rails or
manufacture a new top cover that fits firmly to the bottom
cover. With the old system with its soft plastic units the
whole chassis could flex under hand pressure on the top.
The new design (which is on the ARGOSY 2D) prevents this flexure.
d./ Check that all screws that mount the pto are tight .
e./ Finally, when you put the bottom cover back on , install
the screw that secures to the PTO box FIRST then install the
side screws making sure that the edges of the covers are tight
together. This proceedure ensures that the PTO is part of a
rigid enclosure.
On an ARGOSY 1 that I once owned, I Installed a rigid bearing
plate over the pto shaft to stop it from flexing under hand
weight.
73 Jim VE3DDY
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